1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, particularly to a semiconductor integrated circuit device that operates at a high-speed and yet is energy efficient.
2. Description of the Related Art
A fine microelectronic fabrication technique (fine-fabrication, hereafter) is widely employed in processing chips in order to integrate many functions on a single chip, as described in “Deep-Submicron Microprocessor Design Issues”, IEEE Micro, pp. 11-22, July/Aug., 1999. This fine-fabrication enables many MOS transistors to be integrated on a chip, thereby providing the chip with many functions.
To efficiently integrate many circuits on a chip with fewer defects, however, demands many number of man-hours, namely a long period for developing a plan for such chip. To the contrary, in order to shorten the development period by increasing the number of man-hours causes a shortage of human resources required for designing, thereby causing a bottleneck in designing other types of chips. To solve this dilemma, diversion of developed circuit blocks to other types of chips has been examined.
On the other hand, it is well known that a leakage current (the leakage current includes a sub-threshold leakage current, a gate tunnel leakage current and junction leakage currents such as a GIDL (Gate-Induced Drain Leakage) current) increases due to the fine-fabrication of chip processes. This is described in “Identifying defects in deep-submission CMOS ICs” IEEE Spectrum, pp. 66-71, 1996. Those leakage currents cause the power consumption of a chip to increase. Controlling the supply voltage of a circuit block in its standby state enables the power consumption to be reduced.
Shutting off the supply voltage to the circuit block in the standby state, however, allows the circuit block output node to go into a floating state, causing a penetrating current (short circuit current) to flow in another circuit block that receives the output from the output node. When the circuit block whose supply voltage is controllable is to also be used for another chip, an interface circuit must be designed so as to prevent penetrating currents. This might be an obstacle for re-use of low power-driven circuit blocks.